1. Field of the Invention
The present invention relates generally to a random access memory and, more particularly, but not by way of limitation, to a non-volatile random access memory wherein individual magnetic cells are selectively switched between opposite remanent states.
2. Prior Art Statement
Magnetic materials of various types have been used for many years to form individual, bistable storage elements in memory applications and the like. In general, the individual elements may be either logically or physically distinguishable. In the former category, a substantially homogenous magnetic material is logically partitioned into a plurality of individual storage sites which are mechanically or electrically addressable. Typical of such devices are conventional magnetic disks or tape systems, as well as modern magnetic bubble devices. In the latter category, isolated bodies of magnetic material are physically arranged to facilitate controlled switching and detection of the remanent or permanent state thereof. Typical of such devices are magnetic core, plated wire and magnetic film memories (See, e.g. Chapter 23 of Physics of Magnetism, S. Chikazumi, John Whiley & Sons, Inc., 1966). More recently, magneto-optic memory systems have been developed which use thermomagnetic techniques to switch the remanent state of isolated islands of magnetic film (See, "Magneto-Optic Memory Materials" in Optica Acta, 1977, Vol. 24, Pp. 482-494). Such magneto-optic memory systems have also found use in display applications (See, "Fast Switchable Magneto-Optic Memory-Display Components" by Hill and Schmidt, Philips Journal of Research, 1978, Vol. 33, No.s 5-6, Pp. 211-225; and "Thin-Film Iron Garnet Display Components" by Hill and Schmidt in the Digest of Technical Papers presented at the 1979 SID International Symposiom, First Edition, Pp. 80-81).